Republicans are warning President Obama not to issue an executive order that would require government contractors to disclose their political donations.

Obama drafted the proposal last month, which is reminiscent of a provision in a Democratic bill called the Disclose Act that died in the Congress last year.

That bill would have required corporations and unions to identify themselves in political ads they pay for – a response to a 5-4 Supreme Court ruling that upheld the First Amendment rights of these groups to spend money on campaign ads.

The proposed order would require government contractors to disclose all donations to federal candidates, political parties, committees or interest groups spending money on campaigns once the total exceeds $5,000 in a given year.

The White House has said the proposed order would provide transparency to taxpayers about political spending by government contractors.

But in a letter to the president, California Rep. Kevin McCarthy, the No. 3 Republican in the House, said Obama's proposed order "seems like a blatant attempt to intimidate, and potentially silence, certain speakers who are engaged in their constitutionally protected right to free speech."

Twenty other Republicans signed the letter, which expresses their concern that the effect of the proposed order would be "stifled political speech, as potential and current federal contractors decide to limit their political speech in order to protect their livelihoods.

"While we may often disagree on policy matters, we can surely agree that an open and free political process works best for all," the letter reads.

The Professional Services Council, a trade association that represents more than 330 companies that work with federal agencies, also opposes the order.

"This proposal should never see the light of day," PSC President and CEO Stan Soloway said in a statement. "It is based on dubious legality and a complete lack of awareness of the realities of the federal procurement process."

Soloway added, "This is an ill-conceived proposal that would place government contractors and their senior executives in a unique class. No other individuals or entities, including unions, federal grantees, federal employees, or other business entities, would be subject to such requirements, no matter how reliant they are on government policy or other decisions. It is counterintuitive and will likely be counterproductive."

"Let me be clear: No White House should be able to review your political party affiliation before deciding if you're worthy of a government contract," he said in a statement. "And no one should have to worry about whether their political support will determine their ability to get or keep a federal contract or keep their job."